In hopes of producing oil and gas more efficiently, the petroleum industry continuously strives to improve its recovery systems. As such, those in the industry often drill horizontal, deviated, or multilateral wells, in which several wells are drilled from a main borehole. In such wells, the wellbore may pass through numerous hydrocarbon-bearing zones or may pass for an extended distance through one hydrocarbon-bearing zone. Perforating or “fracturing” the well in a number of different locations within these zones often improves production by increasing the flow of hydrocarbons into the well.
In wells with multiple perforations, however, managing the reservoir becomes difficult. For example, in a well having multiple hydrocarbon-bearing zones of differing pressures, zones of high pressure may force hydrocarbons into zones of lower pressure rather than to the surface. Thus, independent control of hydrocarbon flow from each perforation, or zone of perforations, is important to efficient production.
To independently control hydrocarbon flow from each perforation, or zone of perforations, those of skill in the art have inserted production packers into the well annulus to isolate each perforation. Valves disposed on the production tubing control flow into the tubing from each perforated zone. One type of valve used in the industry for this function is the sliding sleeve valve. Typical sliding sleeve valves are disclosed in U.S. Pat. Nos. 4,560,005, 4,848,457, 5,211,241, 5,263,683, and 6,044,908, which are incorporated by reference herein in their entireties. In such a valve, a sleeve capable of longitudinal movement with respect to the production tube is located between a sleeve housing and the production tube. One or more ports extend radially through the sleeve, the housing, and the production tube. When the sleeve is in an open position, the ports of the sleeve, housing, and production tube are aligned such that fluid may flow through the ports and into the production tube. When the sleeve is in a closed position, the ports of the sleeve are not aligned with the ports on the housing or production tube, preventing fluid flow into the production tube. Although the sleeve can be moved longitudinally between the open and closed positions by several different means, it is common for such control to be hydraulic, essentially pushing the sleeve in a piston-like manner. (Valve control, however, can also be motor-driven or manually actuated).
It is important for production engineers to reliably know the position of a sliding sleeve valve, and particularly to know when the valve is fully opened or closed. Systems exist for continually determining the incremental position of the sleeve along its travel between fully open and full closed, such as are disclosed in the following references, which are incorporated herein by reference: U.S. Pat. No. 5,211,241; U.S. Pat. No. 5,263,683; U.S. patent application Ser. No. 10/339,263, filed Jan. 9, 2003; and U.S. patent application Ser. No. 10/373,146, entitled “Method and System for Determining and Controlling Position of a Valve,” filed Feb. 24, 2003. However, while the ability to incrementally position valves in different hydrocarbon bearing zones allows for greater control of overall fluid production by permitting the creation of pressure drops across certain production zones, such level of control is not always necessary. For example, control of fluid ingress into the valve can be controlled more simply by a “duty cycling” approach, in which the valve is cycled between fully open and fully closed, as discussed in the above-incorporated patent applications. Moreover, such continual-monitoring, incremental position prior art approaches can be complex and expensive to implement.
Accordingly, what is desired is a system and method for reliability determining whether a sliding sleeve valve is fully opened or closed, i.e., a system and method for determining when the sliding sleeve has reached an end point in its position of travel.